1. Field of the Invention
The present invention relates to disk drives and to mobile host devices that may contain disk drives. More particularly, the present invention relates to disk drives and mobile host devices that include a resetable shock sensor.
2. Description of the Prior Art
A typical hard disk drive includes a head disk assembly (“HDA”) and a printed circuit board assembly (“PCBA”). The HDA includes at least one magnetic disk (“disk”), a spindle motor for rotating the disk, and a head stack assembly (“HSA”) that includes a read/write head with at least one transducer for reading and writing data. The HSA is controllably positioned by a servo system in order to read or write information from or to particular tracks on the disk. The typical HSA has three primary portions: (1) an actuator assembly that moves in response to the servo control system; (2) a head gimbal assembly (“HGA”) that extends from the actuator assembly and biases the head toward the disk; and (3) a flex cable assembly that provides an electrical interconnect with minimal constraint on movement.
A typical HGA includes a load beam, a gimbal attached to an end of the load beam, and a head attached to the gimbal. The load beam has a spring function that provides a “gram load” biasing force and a hinge function that permits the head to follow the surface contour of the spinning disk. The load beam has an actuator end that connects to the actuator arm and a gimbal end that connects to the gimbal that carries the head and transmits the gram load biasing force to the head to “load” the head against the disk. A rapidly spinning disk develops a laminar airflow above its surface that lifts the head away from the disk in opposition to the gram load biasing force. The head is said to be “flying” over the disk when in this state.
Within the HDA, the spindle motor rotates the disk or disks, which are the media to and from which the data signals are transmitted via the read write/head on the gimbal attached to the load beam. The transfer rate of the data signals is a function of rotational speed of the spindle motor; the faster the rotational speed, the higher the transfer rate. A spindle motor is essentially an electromagnetic device in which the electromagnetic poles of a stator are switched on & off in a given sequence to drive a hub or a shaft in rotation.
There is huge market potential for putting small form factor disk drives into hand held devices such as cell phones, audio players, PDA, etc. These devices have traditionally used solid-state flash memory to enable their applications. However, flash memory is costly and inherently limited in its storage capacity. Magnetic disk drives, therefore, have emerged as the preferred storage medium for many hand held and mobile devices.
As developed above, disk drives are mechanical in nature and include a rotating disk and moving heads. Accordingly, the robustness of such devices and their ability to survive even moderately severe shock events are justified concerns. Conventionally, such hand held or mobile devices have relied upon various sensors such as accelerometers to detect the shock event (occasioned by a drop, for example) and prepare the device for impact and to regulate spindle rotation, the control signals required to stay on track and the back EMF of motors, for example. However, these sensors are only conventionally operational when there is power to the device. If the hand held or mobile host device is turned off, the device could suffer a shock event, the disk drive (or other constituent components) thereof damaged, and the above-described powered sensors would be ineffective to warn the drive or to initiate special testing to ensure that it is still safe to store data on the drive.
From the foregoing, it may be appreciated that there is a need for disk drives and mobile host devices that include shock sensors that are operational even when the power to the drive or to the host is turned off. This need is all the more pronounced in the case of mobile host devices, as power consumption is often a key consideration in their design.